Some treaties (like with China) are so once sided that the USPS is basically delivering millions of packages from them for free (and our shipping to them in very low).
I think this type of thing pushes local shipping cost and shipping export costs upwards. Because the total cost of deliveries has to be accounted for, so effectively, as a result of receiving large amounts of cheap shipments from China that cannot be billed as highly, these have to be effectively cross subsidised by any other shipments we pay for in our own countries.
It is an odd parallel with the notion that a cheap overseas made product is better to buy than a local one. It looks good in the short term, but when local factories close down and people go out of work, the damage to local economies is not worth it, the unemployed person can then barely afford to buy the cheap imported product.
I guess it is the old argument whether "globalisation" is a good idea or not.
There are a lot of winners and losers in it. I have seen the effects of it destroy local industries in Australia. We once had AWA which made appliances for Australians since 1912. They also built nearly all of RCA's vacuum tubes. When the import tariffs were dropped in the 1970's, AWA ultimately went broke due to imports from Japan and later China. At one point, AWA was manufacturing transistors and IC's too and now we cannot do that here. Also we had a bolt company Ajax Bolts, went bust due to cheap imported bolts & nuts. The iconic Holden car company wast lost too. I think their first model came out in 1948.
One thing now, we cannot design and build own own 5G network here, unless we buy all the IC's / parts from China or buy pre-made equipment. Now the government is worried about spying with imbedded snooping tech in IC's we can barely understand or detect. It is sad to the extent that we have so degraded our own industrial complex by not protecting our borders from cheap imports, that we no longer have as much advanced electronics tech for anyone to spy on and we have become dependent customers.